The present invention relates to an assembly for fastening a circuit card assembly or a module, in place within slots formed in a chassis cold wall. In addition to maintaining the circuit card assembly or module in place, the assembly forms a thermal conductive path to the chassis.
Electronic systems often have their electronic components mounted on circuit boards that are placed in the system by inserting an end connector on the board into a complementary connector socket--usually soldered on an underlying motherboard. Typically, a number of such circuit boards would be positioned in parallel spaced relation to one another.
The lateral edges of the circuit boards are fitted and held in slots formed in a chassis to maintain the circuit boards rigidly in place and, perhaps more importantly, to provide a thermal conductive path from the circuit board to the chassis, allowing the chassis to serve as a heat sink. For this latter purpose, heat sink strips are located at lateral edges of the board. For good thermal conductivity, it is important that the circuit boards be in good thermal contact with the chassis.
Among the techniques to hold the circuit board edges in place in slots formed in the chassis is the use of wedge-clamps. These devices operate to establish and maintain the board-chassis contact and to provide the necessary transfer of heat from the board to the chassis body. An example of such a clamp is shown in U.S. Pat. No. 4,354,770. The wedge-clamp forces edges of the circuit board against one surface of the chassis slot.
Such wedge-clamps are typically located between one edge of the circuit board and a wall of a slot formed in the chassis. Tightening the wedge-clamp forces the board to reference to the chassis slot rather than the (usually underlying) motherboard to which it may be connected. Often, the slots and motherboard connection are not accurately aligned, relative to one another. When misaligned, the board will bend and the connector is stressed, creating a point of possible failure. This becomes a particular problem for circuit boards using metal core surface mount assemblies which are especially susceptible to failure if bent. Thus, to secure the edges of a metal core surface mount assembly requires precise chassis tolerances to locate the slots relative to the underlining motherboard connector to reduce or eliminate bending. This is expensive in terms of both labor and material.
The problem exacerbates when circuits are packaged in module form. Typically such modules have a cube-like housing, containing electronics circuitry mounted on multiple circuit boards. The module also has one or more connectors on one surface for electrical connection to a motherboard or back plane. As with the circuit board, the module includes tabs, usually formed on opposing sides of the module, two or more tabs per side, to fit into the slots in the chassis. As with the circuit card assembly described above, the tab-slot mating surfaces provides both heat transfer paths and placement rigidity to the module. However, the tab-slot alignment for locking the tabs in place with conventional wedge-clamps requires that the module housing and the chassis slots be formed with relatively precise tolerances to obtain a proper fit and locking action. Again, as with circuit boards, this increases the cost (in terms of time, labor and expense) of manufacture of such packaging.